Suppose you are a researcher in a hospital. You are experimenting with a new tranquilizer. You collect data from a random sample of 9 patients. The period of effectiveness of the tranquilizer for each patient (in hours) is as follows: 2.6 2.3 2.8 2.3 2.1 2.3 2.6 2.4 2.3 What is a point estimate for the population mean length of time. (Round answer to 4 decimal places) Which distribution should you use for this problem? O normal distribution O t-distribution What must be true in order to construct a confidence interval in this situation? O The sample size must be greater than 30 O The population standard deviation must be known O The population must be approximately normal O The population mean must be known Construct a 90% confidence interval for the population mean length of time. Enter your answer as an open- interval (i.e., parentheses) Round upper and lower bounds to two decimal places What does it mean to be "90% confident" in this problem? 90% of all simple random samples of size 9 from this population will result in confidence intervals that con tain the population mean O The confidence interval contains 90% of all samples O There is a 90% chance that the confidence interval contains the population mean